(a) Field of the Invention
The present invention relates to an air-foil bearing. More particularly, the present invention relates to an air-foil bearing which enables a simple configuration thereof, and enhances axis direction supporting capability and durability and mounting to a small rotating body such as a compressor or a turbine, to which mounting of a bearing is impossible or difficult.
(b) Description of the Related Art
In general, a machine having a rotating shaft provided thereto, such as a generator and a turbine, is provided with a thrust bearing for reducing axial direction vibration, together with a radial bearing for reducing radial direction vibration.
Particularly, in a case of the rotating body which rotates at a fast speed, along with the vibration reducing effect, the thrust bearing is required to be able to be used at a high temperature, and to have high durability for preventing the bearing from being damaged by an axis direction load.
Due to such conditions, in general, a fluid bearing or a bearing of a mode in which a fluid that serves as a lubricant is supplied to the bearing has been widely used as the thrust bearing.
However, in a case of a small machine such as a micro-gas turbine, although the small machine is required to rotate at a high speed for obtaining a desired output, the small machine is not suitable for connecting to a lubricant supplier thereto due to problems such as a volume thereof.
The fast rotating body is required to have a damping effect on the vibration generated due to the fast rotation, to be able to be used at a high temperature, and to have durability for preventing a bearing from being damaged by the axial direction load, thereby leading to demand for a non-contact oilless thrust bearing, which is becoming higher day by day.
The demand has led to suggestions regarding different non-contact oilless thrust bearing technologies, such as an air-foil bearing and an electro-magnetic bearing as typical examples.
As for the air-foil bearing, Korea Patent Registration No. 1204194 discloses “GAS-FOIL THRUST BEARING AND CENTRIFUGAL COMPRESSOR HAVING THE SAME”, and as for the electro-magnetic bearing, U.S. Patent Laid-Open Publication No. 2009-0039740 discloses “MAGNETIC BEARING”.
However, since the non-contact oilless thrust bearing has a complicated configuration to cause difficulty in manufacturing, particularly in manufacturing small-sized bearings with a diameter below 300 mm, and to have difficulty in improving manufacturing process accuracy, the non-contact oilless thrust bearing has problems in that productivity is poor and the bearing is expensive.
Particularly, a high axial direction thrust is liable to cause deformation of the air-foil thrust bearing to cause a problem of reducing a function of the bearing.
In the meantime, since the thrust bearing has an axial supporting direction, which is different from the radial direction of the radial bearing, the thrust bearing and the radial bearing are configured to have separate systems.
Since it is required to assemble two kinds of bearings after separately manufacturing them, while requiring a separate back plate for attaching the thrust bearing, which makes the manufacturing process complicated, steps for meeting assembly accuracy are required at the time of assembly.
Moreover, the air-foil bearing to be applied to the thrust bearing has a problem of having a very low axial direction load limitation.
Along with this, a process is required for manufacturing a complicated bump shape, and welding the thrust foil and the bump to a bearing housing.
That is, since the thrust bearing and the radial bearing have separate systems, a problem is caused in which the volume of a bearing portion is inevitably increased.
Particularly, there has been a problem in that, since the volume is increased when the radial bearing and the thrust bearing are applied, the small-sized rotating body having a compressor or turbine impeller must have the thrust bearing mounted to a back plate portion of the turbine or impeller for increasing a first bending mode.
Moreover, since the two kinds of bearings are required to be fabricated individually, a problem is caused in which the fabrication and assembly are complicated.
Along with this, mounting or assembly of an integrated bearing to the small rotating body, such as the compressor or the turbine, is impossible or difficult.
In order to solve above problems, U.S. Pat. No. 7,134,793 discloses “Thrust Bearing Assembly” which suggests a bearing assembly.
However, since the invention is limited to the thrust bearing which is not included to the non-contact oilless thrust bearing, the invention has a problem in that bearing durability for the axial direction load cannot be assured at the time of fast speed rotation.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.